Direct current amplifier circuits



April 11, 1939.

R. GURTLER DIRECT CURRENT AMPLIFIER CIRCUITS Filed Aug. 3, 1935 AAAAAIA "VIII" our/ 07 ll ll E fil n W llllAAl lAAAAlL INVENTOR RUDOLF URTLER BY WZM ATTORNEY Patented Apr. 11, 1939 UNITED STATES 2,153,752 DIRECT CURRENT AMPLIFIER CIRCUITS Rudolf Giirtler,

Berlin, Germany, assignor to Telefunken Gescllschaft fiir Drahtlose Telegraphic m. b. H., Berlin, Germany, a corporation of Germany Application August 3, 1935, Serial No. 34,523

In Germany 3 Claims.

In direct current amplifiers known in the prior art the output terminals present a certain potential difference in reference to the input terminals which is a function of the nature of the 5 circuit organization and the size of the sources of potential. The present invention is concerned with a direct current amplifier in which the output and the input are independent of each other so far as the potential differences with respect to a fixed reference point is concerned.

In the drawing:

Fig. 1 shows a fundamental embodiment of the invention,

Fig. 2 show a modification,

Fig. 3 illustrates the amplifier characteristics of the circuit of Fig. 2,

Fig. 4 is a circuit diagram of an amplifier control circuit using the invention.

The fundamental circuit scheme of such an amplifier is illustrated in Fig 1. Referring to the drawing, 1 denotes an amplifier tube, the plate end of which is fed from an alternating current source 3. The potential to be amplified is impressed upon the grid circuit by way of the terminals e, e which, if desired, may include a biasing voltage source 2. In the plate circuit is included a transformer 4 which by way of the valve 5 sets up a direct current voltage across the capacity 6 which may be taken off across the terminals a, a. By the provision of the said transformer 4, conditions are made such that the output terminals a, a, are perfectly isolated from the input terminals e, e, so far as voltage with respect to a fixed reference point is concerned.

In the exemplified embodiment of the invention shown in Fig. 2, two amplifier tubes l and- 1 are connected push-pull fashion at the anode or plate end, while they are connected in parallel at the grid end. The preferable plan would be to use a symmetric circuit scheme also in the rectifier circuit, say, a full-wave rectifier as indicated in Fig. 2 (valves 5 and ill).

Fig. 3 shows the amplifier characteristic of an amplifier arranged in accordance with the scheme in Fig. 2. The abscissa stands for the resultant grid voltage at the amplifier tubes I and I, while the ordinate stands for the useful voltage Un delivered across the terminals a, a. The portion of the characteristic between points C and D is practically straight, while the lower end is curved as expected from the tube characteristic. Inasmuch as the general demand is for the existence of a linear dependence of the output potential upon the input potential, only the part CD of the characteristic will be suitable. Hence, the

August 8, 1934 biasing potential 2 must be so chosen that the resultant grid voltage lies between the values and 0A, and thus the output potential between the values OC and AD.

voltage could be included so that the absolute values may be adjusted at will. Then the voltage variation will correspond to the characteristic CD, Fig. 3.

Fig. 4 shows a circuit organization in which a direct current amplifier of a kind hereinbefore described is employed. H is the tube of an amplifier which, under normal operating conditions, is occasionally worked within the grid-current region of its characteristc to a greater or lesser extent. The alternating potential to be amplified is fed to tube It by way of the transformer l3; i8 is an output transformer, I4 is the grid blocking condenser, and IS the plate blocking condenser. 62 is a regulator tube which receives its plate current from the direct current source IS. The fall of potential produced across the resistance 15 represents the biasing voltage for the amplifier tube II. If, then, tube H is operated so that there will be a flow of grid current, the grid direct current of tube H will also flow by way of the resistance l and thus alter the biasing voltage.

However, in order that the biasing voltage may be stabilized and kept constant, a resistance i1 is included in the grid direct current circuit of tube I l across which is set up a voltage proportional to the grid direct current which is impressed upon the grid circuit of the regulator tube I2 by way of an amplifier based upon the principle hereinbefore described.

The direct current amplifier comprises the two tubes l and I, and they are fed at the plate end by way of the transformers 8 and Ba, respectively. The direct current voltage is fed by way of a filter system 6, 5a, 6b, to the resistance 9. The grid circuit of the tube 12 includes a voltage which is tapped on the resistance 20, and which is thus proportional to the plate direct current voltage Us. of tube H. This voltage by way of tube 12 varies the voltage across resistance H3 in proportion to the plate voltage Us. In this manner, the plate current flow of tube II is stabilized in spite of such variations as may happen in the supply of plate direct current voltage Us.- If, then, the fall of potential increases at H, the grid biasing voltage of tube [2 becomes so much more markedly negative that the plate current of this tube decreases to such a degree that the fall of voltage across resistance l5 and. re-

It goes without saying D that in the output circuit a constant additional sistor I! has the same value as before the said increase across resistor I! so that the grid biasing potential of tube l l remains unvaried.

Upon the incipient flow of grid direct current in the grid circuit of tube H, the voltage at I5 must be so set that all of the falls of potential in the grid circuit of the tube II will always result in the original grid biasing voltage. In the circuit organization shown in Fig. 4, it is thus feasible to stabilize or regulate the grid biasing voltage of an amplifier in the presence of grid current flow. The direct current amplifier (I, l, 4) comprised in the circuit arrangement, and which operates in accordance with the basic idea of this invention, has the purpose and function of making available, in amplified form, at some other place (across resistance 9), a direct current voltage arising across resistance H, the said point of delivery presenting to a datum or reference point (ground 0) another potential.

If in connection with the above-mentioned direct current amplifier, high amplification of the direct current voltage, or a high output energy, is required, the same could be equipped with a few additional amplifying stages. The external resistance of the direct current amplifier need not comprise merely an output transformer. If necessary, a capacity could, for instance, be connected in parallel relation to the transformer.

What I claim is:

1. In combination with a source of direct current potential to be amplified, an amplifier tube having its input electrodes coupled to said source, a source of alternating current coupled to the output electrodes of the tube, a rectifier, a transformer coupling the output circuit of the amplifier and the rectifier and transmitting to the latter an alternating potential modulated by said direct current, said rectifier being connected solely to the secondary of said transformer and means in circuit with the rectifier for smoothing a uni-directional voltage developed from the rectified modulated alternating currents.

2. In combination with a source of direct current potential to be amplified, an amplifier tube having its input electrodes coupled to said source, a source of alternating current coupled to the output electrodes of the tube, a rectifier, a transformer coupling the output circuit of the amplifier and the rectifier and transmitting to the latter an alternating potential modulated by said direct current, said rectifier being connected sole- 1y to the secondary of said transformer and means in circuit with the rectifier for smoothing a] uni-directional voltage developed from the rectified modulated alternating currents, a second amplifier tube having its input electrodes in parallel with the first tube input electrodes, and its output electrodes in push-pull relation with the first tube output electrodes 3. In combination wth a source of direct current potential to be amplified, an amplifier tube having its input electrodes coupled to said source, a source of alternating current coupled to the output electrodes of the tube, a rectifier, means coupling the output circuit of the amplifier and the rectifier and transmitting to the latter an alternating' potential modulated by said direct current, and means in circuit with the rectifier for developing a uni-directional voltage from the rectified modulated alternating currents, a second amplifier, a som'ce of alternating potential coupled to the input electrodes thereof, an output circuit coupled to the output electrodes of the second amplifier, a resistor connected between the last input electrodes developing a direct potential from a direct current flow therethrough, said last resistor being coupled to the input electrodes of the first amplifier and comprising said first named source, and means, responsive to the rectifier uni-directional voltage, for regulating the potential difierence between the input electrodes of said second amplifier.

RUDOLF GURTLER. 

